Pregnancy Week Calculator
Enter the first day of your last period, or your due date if you already have one. The calculator shows how many weeks and days pregnant you are today, your trimester and how long is left.
Free, no sign-up. What you enter stays in your browser: it is not saved or sent to HerFound. Reviewed .
Work it out from
Enter the first day of your last period to see how many weeks pregnant you are.
This is general information, not medical advice. It cannot take your own health history into account. For anything that worries you, speak to a doctor, midwife or pharmacist.
How it works
Pregnancy is counted from the first day of your last period, not from conception. Weeks pregnant = the number of days since that day, divided by 7. The days left over are the extra days, so 74 days is 10 weeks and 4 days.
If you enter a due date, the calculator works backwards. A due date is 280 days (40 weeks) after the first day of the last period, so it subtracts 280 days from the due date and counts from there.
The second trimester starts at 14 weeks and the third at 28 weeks. Percent complete is the days so far divided by 280.
What it cannot tell you
- A date from your last period assumes a 28-day cycle with ovulation on day 14. If your cycle is longer, shorter or irregular, the real number can differ by several days.
- A dating ultrasound in the first trimester is more accurate than period dates. If your clinic gave you a due date, choose the due date method and enter theirs.
- The 40 weeks is an average. Most babies are born between 37 and 42 weeks, so the percent complete is a rough guide and not a countdown to the birth.
Apps that do this for you
A calculator answers once. These apps keep track over time. Compare all pregnancy and parenting apps.
Baby Connect
A baby tracker: log sleep, feeds and diapers and share it with every caregiver, on phone, web and Apple Watch.
Baby Daybook
A baby tracker: feeds, sleep, nappies and growth, with sleep predictions and family sync
BabyCenter
A pregnancy and baby tracker: week-by-week updates, handy tools, articles and a parent community.
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Common questions
You are as many weeks pregnant as the number of full weeks since the first day of your last period. Count the days from that date to today and divide by 7. For example, 70 days after the first day of your last period you are 10 weeks pregnant.
Pregnancy weeks are counted from the first day of the last period, which is about 2 weeks before conception. So on the day of a missed period you are already called 4 weeks pregnant. Doctors and midwives use this count because the period date is usually known and the conception date is not.
To work out weeks pregnant from a due date, subtract 280 days from the due date and count the days from there to today. Another way is to count the days left until the due date, subtract that from 280 and divide by 7. With 84 days to go you are 28 weeks pregnant.
The first trimester runs from week 0 to the end of week 13. The second trimester starts at 14 weeks and the third trimester starts at 28 weeks. Some sources place the lines a few days earlier or later, so your clinic may use slightly different dates.
No, week 10 and 10 weeks pregnant are slightly different. At 10 weeks pregnant you have completed 10 full weeks and are in the 11th week of pregnancy. It works like a birthday: a one-year-old child is in their second year.